Dome reflector/ES fitting. What is this wire for?

[user 30368]

I bought this dome reflector and ES fitting and was told to simply un-screw the ES fitting, whack the dome between it, and then screw it back together. The ES fitting was pre-wired with the power cord. Whats the extra wire hanging out the side for??
Also, it has one rubber seal. does that go on the outter part of the dome or the inner part?

 

[grizz]

That is your earth, ground it to your enclosure.

 

[user 30368]

excuse my blondness - the dome is going to be hanging in the air over my bobtail. Does it screw into that little hole on the dome?? Looks like a good spot to put it if you ask me!